A short-term screening system is designed to discover potential inhibitors for the chemical carcinogenesis of N-nitrosamines and to elucidate the structural features required for inhibitory activity. The carcinogenic N-nitrosamines of important environmental implications to be used are: N-nitrosopyrrolidine (NPYR); N'-nitrosonornicotine (NNN); 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK); N-nitrosomorpholine (NMOR); and dimethyl nitrosamine (DMN). Dietary-related inhibitors of chemical carcinogenesis such as BHA (food antioxidant), cinnamic acids, coumarins, aromatic isothiocyanates, and indoles (plant and vegetable constituents) and their derivatives, totaling 32 compounds, will be tested for their inhibitory activity. The potential inhibitory activity of each compound will be determined using three sets of experiments designed to evaluate its ability to decrease the metabolic activation and increase metabolic detoxification of the nitrosamines. These experiments include: (1) In vitro metabolism; (2a) In vivo metabolism; (2b) In vivo formation of DNA-carcinogen adducts; and (3) Induction of DNA repair. Compounds passing these experiments and demonstrating the most promising inhibitory activity will be chosen for animal bioassays.